In a related-art air-conditioning apparatus, such as a multi-air-conditioning apparatus for a building, refrigerant is circulated between an outdoor unit, functioning as a heat source unit, disposed outside a structure, for example, and an indoor unit disposed in an indoor space in the structure. The refrigerant transfers or removes heat to or from air to heat or cool the air, thus heating or cooling an air-conditioned space with the heated or cooled air. As regards the refrigerant used in such an air-conditioning apparatus, for example, a hydrofluorocarbon (HFC) refrigerant is often used. An air-conditioning apparatus recently developed uses a natural refrigerant, such as carbon dioxide (CO2).
In an air-conditioning apparatus called a chiller, cooling energy or heating energy is produced in a heat source unit disposed outside a structure. Water, antifreeze, or the like is heated or cooled by a heat exchanger included in an outdoor unit and it is conveyed to a fan coil unit or a panel heater, serving as an indoor unit, to perform heating or cooling (refer to Patent Literature 1, for example).
An air-conditioning apparatus called an exhaust-heat recovery chiller is configured such that a heat source unit is connected to each indoor unit by four water pipes arranged therebetween and, for example, cooled water and heated water are simultaneously supplied to the indoor units so that cooling or heating can be freely selected in each indoor unit (refer to Patent Literature 2, for example).
Another air-conditioning apparatus recently developed is configured such that a heat exchanger for a primary refrigerant and a secondary refrigerant is disposed near each indoor unit to convey the secondary refrigerant to the indoor unit (refer to Patent Literature 3, for example).
Still another air-conditioning apparatus recently developed is configured such that an outdoor unit is connected to each branching unit including a heat exchanger by two pipes and a secondary refrigerant is conveyed to an indoor unit (refer to Patent Literature 4, for example).
Air-conditioning apparatuses, such as a multi-air-conditioning apparatus for a building, include an air-conditioning apparatus configured such that refrigerant is circulated from an outdoor unit to a relay unit and a heat medium, such as water, is circulated from the relay unit to each indoor unit to reduce conveyance power for the heat medium while circulating the heat medium, such as water, through the indoor unit (refer to Patent Literature 5, for example).